Lamb, in what country are you located?
I am in the US. I was supplied with plenty of samples of various items before leaving the hospital, and then the ostomy nurse gave me lots more. Before I left the hospital, I had signed off on forms to get samples from the various supply companies. In addition, I have found that the major companies are all happy to send out more samples as you identify your preferences and needs, and will often ship things overnight if you are in a pinch. (They are competing for our business, which has some aspects to our advantage!)
Your ostomy burse, at the pre-op appointment, will likely ask you to sit, and stand, and bend over while holding an appliance to your belly, so that it is located in the best spot for you. (If they don't suggest bending over and sitting, you can suggest it!